1. Field of the Invention
The present invention is related to a wireless communication, more particularly to a method of performing a random access procedure in a multiple-component carrier system.
2. Related Art
In a common wireless communication system, although the bandwidth of uplink and the bandwidth of downlink are differently set up, only one carrier is taken into consideration. Even in 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), the number of carriers constituting uplink and downlink is 1, and the bandwidth of uplink and the bandwidth of downlink bandwidth are in general symmetrical to each other on the basis of a single carrier. However, it is not easy to allocate a large frequency bandwidth except some regions in the world. Accordingly, in order to efficiently use small sliced bands, a carrier aggregation technique for producing the same effect as that a logically large band is used by binding a plurality of physically non-continuous bands in the frequency domain is being developed. The carrier aggregation technique includes, for example, a technique in which system bandwidth of 100 MHz is supported by using multiple component carriers.
A user equipment (UE) shall perform random access procedure to gain access to a network. The random access procedure is accomplished through a Random Access Channel (RACH), i.e., an uplink transmission channel. The UE transmits an initial control message (i.e. preamble) to the network through the RACH. The aim of performing the random access procedure is to obtain time synchronization between the UE and the network or to obtain radio resources for uplink transmission.
When radio resource control (RRC) layer of the UE receives a random access problem such as a random access failure, the UE considers radio link failure to be detected and so initiates the connection re-establishment procedure in which case the UE sends the RRC connection re-establishment request message to a base station (BS) in order to recover the connection to the network.
Because multiple uplink component carriers (CCs) can be aggregated, the UE can perform a random access procedure on one uplink CC or on another CC, even possibly on both CCs.
When a random access response corresponding to a random access preamble is not received by the UE or contention resolution is not successful, a random access problem occurs. Accordingly, a method of effectively handling this random access problem in multiple-component carrier system is required.